Chain tensioner

ABSTRACT

To provide a chain tensioner that has a simple structure, is universally usable, is capable of supplying sufficient and necessary oil when restarted after a long time after the stop of oil supply, enables reduction in entire length and size, and enables easy production and reduction in production cost. An urging unit  140  provided in an oil pressure chamber  101  to be expandable and contractible urges a plunger  120  outward from a plunger bore  111  in a tensioner body  110  of the chain tensioner  100 . The plunger  120  includes a plunger body  126 , a check valve  150  provided inside the body, and a reserve tube  130  that has an oil reservoir chamber  123  communicating with the oil pressure chamber  101  through an oil hole  132.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a chain tensioner that includes atensioner body having a cylindrical plunger bore with an open end, acylindrical plunger slidable within the plunger bore, and an urging unitaccommodated inside an oil pressure chamber formed between the plungerbore and the rear end of the plunger such as to be able to expand andcontract and to urge the plunger outward, the chain tensioner beingcapable of maintaining suitable tension of a chain.

2. Description of the Related Art

Chain tensioners are commonly used for maintaining suitable tension ofchains. In a chain guide mechanism that slidably guides a transmissionchain such as an endless roller chain passing over respective sprocketsof a crankshaft and a cam shaft inside an engine room with a guide shoe,for example, it is known to urge a pivoting chain guide having the guideshoe with a chain tensioner to maintain suitable tension.

For example, as shown in FIG. 16, an endless timing chain CH passes overa drive sprocket S1 attached to a crankshaft and a pair of drivensprockets S2 and S3 attached to cam shafts in an engine room. A chainguide mechanism has a pivoting chain guide G1 and a stationary chainguide G2 for guiding this timing chain CH.

The stationary chain guide G2 is fixed in position in the engine roomwith two mounting shafts B1 and B2, while the pivoting chain guide G1 isattached in the engine room such as to be pivotable around the mountingshaft BO in the plane in which the timing chain CH runs.

The chain tensioner 500 maintains the tension of the timing chain CH ata suitable level as well as reduces its vibration by pressing thepivoting chain guide G1.

The known chain tensioner 500 used in such a chain guide mechanismincludes, for example, as shown schematically in FIG. 17, a tensionerbody 510 having a cylindrical plunger bore 511 with an open end, acylindrical plunger 520 in the plunger bore 511 to slide against thecylindrical surface 513 of the plunger bore 511, and urging means thaturges the plunger 520 outward from the plunger bore 511.

The urging means is a coil spring 540 accommodated inside a cylindricalrecess 521 in the cylindrical plunger 520 and compressed between theplunger and the bottom 512 of the plunger bore 511.

Oil is supplied from an oil supply hole 514 formed in the plunger bore511, so that an oil pressure chamber 501 formed between the plunger bore511 and the plunger 520 is filled with oil, which oil urges the plunger520 outward. A check valve 550 (schematically shown as a check ball)stops the oil from flowing out from the oil supply hole 514.

As the plunger 520 reciprocates, oil flows through the small gap betweenthe plunger 520 and the plunger bore 511, and the flow resistanceprovides the damping effect of slowing down the reciprocal movement ofthe plunger 520.

In such a known chain tensioner 500, when let stand for a long timeafter the oil supply is stopped (in the case with an engine, after theengine is stopped), there is a time lag before oil is suppliedimmediately after the next start-up, and as no oil is replenished butthe oil in the oil pressure chamber 501 leaks out when the plunger 520moves back and forth, there occurs a shortage of oil in the oil pressurechamber 501. Because of this shortage of oil, the damping force of theoil does not act on the plunger 520, which may sometimes lead tovibration and abnormal noise of the timing chain C, or damage the timingchain C.

It is also known to provide an oil reservoir chamber inside the plungerconfigured to supply oil into the oil pressure chamber (see JapanesePatent Application Laid-open No. H09-177907 and Japanese PatentPublication No. 4376278). A constant amount of oil is retained in theoil reservoir chamber, so that, even immediately after the start-upafter a long non-use time, oil remaining in the oil reservoir chamber issupplied to the oil pressure chamber, to maintain the damping force ofoil for the plunger and to prevent vibration or damage of the chain.

With the technique described in Japanese Patent Application Laid-openNo. H09-177907, however, most of the oil supplied from the oil reservoirchamber (oil reserve chamber 9) into the oil pressure chamber (highpressure chamber 14) leaks out from the oil pressure chamber (highpressure chamber 14) through the gap between the plunger and the plungerbore (plunger chamber 4) as the plunger reciprocates immediately afterthe start-up, and leaks out from the oil supply hole (supply hole 12) orfrom the distal end of the plunger, so that the amount of oil in the oilreservoir chamber (oil reserve chamber 9) is reduced.

It is therefore necessary for the oil reservoir chamber (oil reservechamber 9) to have a large capacity so as to keep enough oil insideduring the time lag before oil is supplied from the oil supply hole(supply hole 12) immediately after the start-up, because of which theentire tensioner could not be made shorter and could hardly be madesmaller.

With the technique described in Japanese Patent Publication No. 4376278,the oil supply hole (oil supply hole 122) is arranged in an upper partand oriented diagonally forward so that at least the oil that has leakedfrom the oil pressure chamber (high pressure oil chamber R) through thegap between the plunger and the plunger bore is prevented from leakingthrough the oil supply hole (oil supply hole 122) to the outside.

However, this configuration cannot be applied to a design in which oilis supplied laterally. Universal use of the tensioner was difficultbecause of the restrictions on the position of the oil supply hole (oilsupply hole 122) or mounting orientation of the chain tensioner.

As the oil inevitably leaks out from the distal end of the plunger, thetensioner needs to have an oil reservoir chamber with a large volume aswith the technique described in Japanese Patent Application Laid-openNo. H09-177907, because of which the entire tensioner could not be madeshorter and could hardly be made smaller.

Another problem was that the plunger structure was made complex becauseof the anti-rotation mechanism that was essential to stop rotation ofthe plunger.

The plunger features such as the oil reservoir chamber and oil supplyhole in the known technologies of Japanese Patent Application Laid-openNo. H09-177907 or Japanese Patent Publication No. 4376278 were formed bymachining a one-piece plunger. The production process was thereforecomplex because the plunger needed machining in many parts, and also thecost was increased because of material limitations.

SUMMARY OF THE INVENTION

The present invention is directed to solve these problems, and aims toprovide a chain tensioner that has a simple structure, is universallyusable, is capable of supplying sufficient and necessary oil whenrestarted after a long time after the stop of oil supply, enablesreduction in entire length and size, and enables easy production andreduction in production cost.

The present invention solves the problems described above by providing achain tensioner including: a tensioner body having a cylindrical plungerbore with an open end; a cylindrical plunger slidable within the plungerbore; and an urging unit accommodated inside an oil pressure chamberformed between the plunger bore and a rear end of the plunger such as tobe able to expand and contract and to urge the plunger outward, theplunger including a plunger body, a check valve and a reserve tubeprovided inside the plunger body, the reserve tube having an oil holeformed on the check valve side and an oil reservoir chambercommunicating with the oil pressure chamber through the oil hole.

With the chain tensioner according to claim 1, a check valve and areserve tube are provided inside the plunger body, and the reserve tubehas an oil hole on the check valve side and an oil reservoir chamberthat communicates with an oil pressure chamber through the oil hole. Asthe reserve tube functions as a stationary seat for the check valve, theplunger body can have a simple internal shape. The need of complexmachining is thus obviated and a large space is formed for the oilreservoir chamber.

This way, sufficient and necessary oil can be supplied when restartedafter a long time after the stop of oil supply, the production is madeeasy and the production cost is reduced, and the entire length and sizeof the tensioner are reduced.

With the structure as set forth in claim 2, oil supplied from the oilsupply hole flows from the supply chamber and through the internalsupply cavity on the outer circumference of the reserve tube, andreaches the oil pressure chamber through an oil communication notchformed at the distal end in the outward direction of the plunger of thereserve tube. Therefore, the amount of oil that remains in the oilreservoir chamber can be increased irrespective of the position of theoil supply hole or the mounting orientation of the chain tensioneritself, or of the rotational position of the plunger.

This way, sufficient and necessary oil can be supplied when restartedafter a long time after the stop of oil supply, as well as the plungerstructure is simplified, as the need of the mechanism for stoppingrotation of the plunger is obviated.

With the structure as set forth in claim 3, as an outer leak groove isformed in the outer circumferential surface of the plunger body on theoil pressure chamber side such as to extend from the oil pressurechamber to the supply chamber, when the plunger reciprocates immediatelyafter the start-up after being stopped for a long time, oil is suppliedfrom the oil reservoir chamber to the oil pressure chamber via the checkvalve, wherein most of the oil in the oil pressure chamber passesthrough the outer leak groove, and is recovered into the oil reservoirchamber through the supply chamber, plunger hole, internal supplycavity, and oil communication notch.

Therefore, the amount of oil leaking to the outside from the distal endof the plunger through the gap between the plunger and the plunger boreis reduced irrespective of the position of the oil supply hole or themounting orientation of the chain tensioner itself, so that much moreoil can be recovered into the oil reservoir chamber from the plungerhole that opens to the supply chamber.

Therefore, even though there is little oil left in the oil reservoirchamber after the stop of oil supply, a sufficient and necessary amountof oil can be secured for the next start-up by reducing the amount ofoil leaking outside and by circulating and recovering the oil from theoil pressure chamber into the oil reservoir chamber, which enables theoil reservoir chamber to have a smaller space, and the entire tensionerto be shorter and smaller.

The chain tensioner is more universally usable, as less oil leaksoutside and more oil is recovered into the oil reservoir chamberirrespective of the position of the oil supply hole or the mountingorientation of the chain tensioner itself.

With the structure as set forth in claim 4, as the outer leak groove islocated at a circumferentially same phase position as the plunger hole,more of the oil leaking through the outer leak groove into the supplychamber flows directly toward the plunger hole with the reciprocation ofthe plunger, so that more oil is recovered into the oil reservoirchamber through the plunger hole, internal supply cavity, and oilcommunication notch instead of leaking to the outside.

With the structure as set forth in claim 5, as an inner leak groove isformed in the outer circumferential surface of the reserve tube on thecheck valve side such as to extend from the oil pressure chamber to theinternal supply cavity, when the plunger reciprocates, oil is suppliedfrom the oil reservoir chamber to the oil pressure chamber via the checkvalve, and the oil in the oil pressure chamber is directly recoveredinto the oil reservoir chamber through the inner leak groove.

Therefore, the amount of oil leaking to the outside from the distal endof the plunger through the gap between the plunger and the plunger boreis further reduced irrespective of the position of the oil supply holeor the mounting orientation of the chain tensioner itself, orirrespective of the rotational position of the plunger, so that muchmore oil can be recovered into the oil reservoir chamber.

With the structure as set forth in claim 6, as a contact surface leakgroove is formed in at least one of the opposite surfaces of the reservetube and the check valve such as to extend from the oil pressure chamberto the oil reservoir chamber, when the plunger reciprocates, oil issupplied from the oil reservoir chamber to the oil pressure chamber viathe check valve, and the oil in the oil pressure chamber is directlyrecovered into the oil reservoir chamber through the contact surfaceleak groove.

Therefore, the amount of oil leaking to the outside from the distal endof the plunger through the gap between the plunger and the plunger boreis further reduced irrespective of the position of the oil supply holeor the mounting orientation of the chain tensioner itself, or of therotational position of the plunger, so that much more oil can berecovered into the oil reservoir chamber.

The distance of the contact surface leak groove can be made longer asappropriate, so that the flow resistance can be set in a wider range asrequired.

With the structure as set forth in claim 7, the other end of the coilspring is seated in the plunger body, so that there is no need toprovide a long space for the oil pressure chamber in the plunger bore toaccommodate the coil spring, and the entire tensioner can be madeshorter and smaller.

With the structure as set forth in claim 8, the other end of the coilspring is seated on the outer flange of the retainer in the plungerbody, so that the check valve can be disposed inside the coil spring. Asthere is no need to provide a long space for the oil pressure chamber inthe plunger bore, the entire tensioner can be made shorter and smaller.

With the structure as set forth in claim 9, one surface on the checkvalve side of the reserve tube functions also as the ball seat of thecheck valve. As the structure is further simplified, production iseasier and the production cost can be reduced.

With the structure as set forth in claim 10, one end of the coil springseated on the bottom of the plunger bore is restricted from movingsideways by the tapered surface, so that looseness or displacement ofthe coil spring in the lateral direction inside the oil pressure chamberor the cylindrical recess can be prevented to allow smooth reciprocationof the plunger. Also, as the tensioner requires less space for allowinglateral displacement, it can be made shorter and smaller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a chain tensioner according to a firstembodiment of the present invention;

FIG. 2 is a plan view of the chain tensioner according to the firstembodiment of the present invention;

FIG. 3 is a side view of the chain tensioner on one side where a plungerprotrudes according to the first embodiment of the present invention;

FIG. 4 is a cross-sectional view along B-B of FIG. 2;

FIG. 5 is a cross-sectional view along A-A of FIG. 1;

FIG. 6 is a cross-sectional view of only the tensioner body of FIG. 4;

FIG. 7 is a cross-sectional view of only the tensioner body of FIG. 5;

FIG. 8 is a cross-sectional view of only the plunger body of FIG. 4;

FIG. 9 is a perspective view of a reserve tube of the chain tensioneraccording to the first embodiment of the present invention;

FIG. 10 is a cross-sectional view of the chain tensioner according to asecond embodiment of the present invention (section along B-B of FIG.2);

FIG. 11 is a perspective view of a reserve tube of the chain tensioneraccording to the second embodiment of the present invention;

FIG. 12 is a cross-sectional view of the chain tensioner according to athird embodiment of the present invention (section along B-B of FIG. 2);

FIG. 13A is a perspective view of a reserve tube of the chain tensioneraccording to the third embodiment of the present invention;

FIG. 13B is a perspective view of a ball seat of the chain tensioneraccording to the third embodiment of the present invention;

FIG. 14 is a cross-sectional view of the chain tensioner according to afourth embodiment of the present invention (section along B-B of FIG.2);

FIG. 15 is a cross-sectional view of the chain tensioner according to afifth embodiment of the present invention (section along B-B of FIG. 2);

FIG. 16 is a diagram illustrating the chain tensioner used in a chainguide mechanism of an engine; and

FIG. 17 is a schematic diagram illustrating a conventional chaintensioner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The chain tensioner of the present invention may be embodied in anyspecific form as long as: it includes a tensioner body having acylindrical plunger bore with an open end, a cylindrical plungerslidable within the plunger bore, and an urging unit accommodated insidean oil pressure chamber formed between the plunger bore and a rear endof the plunger such as to be able to expand and contract and to urge theplunger outward, the plunger including a plunger body, a check valve anda reserve tube provided inside the plunger body, the reserve tube havingan oil hole formed on the check valve side and an oil reservoir chambercommunicating with the oil pressure chamber through the oil hole; and aslong as it has a simple structure, is universally usable and capable ofsupplying sufficient and necessary oil when restarted after a long timeafter the stop of oil supply, enables reduction of its entire length andsize, and enables easy production and reduction of production cost.

For example, the reserve tube may be made of any material, preferablyaluminum or resin so as to reduce the overall weight, inertial mass ofthe plunger, and production cost.

Since the inside shape of the plunger body is simplified, it may be madeby press-forming or the like from a metal sheet blank.

<Embodiment 1>

A chain tensioner 100 according to a first embodiment of the presentinvention will be described with reference to the drawings.

The chain tensioner 100 according to a first embodiment of the presentinvention includes, as shown in FIG. 1 to FIG. 8, a tensioner body 110having a cylindrical plunger bore 111 with an open end, a cylindricalplunger 120 slidable within the plunger bore 111, and a coil spring 140that is an urging unit accommodated inside an oil pressure chamber 101formed between the plunger bore 111 and the rear end of the plunger 120such as to be able to expand and contract and to urge the plunger 120outward.

The chain tensioner 100 according to this embodiment is securely mountedinside an engine having a chain guide mechanism. For this purpose, thetensioner body 110 has mounting parts 116 with mounting holes 117 forbolts or the like to pass through as shown in FIG. 1 to FIG. 6.

An oil supply hole 114 is formed in the cylindrical surface 113 of theplunger bore 111 of the tensioner body 110 as shown in FIG. 5 to FIG. 7,which opens to outside so that oil can be supplied.

Near the opening of the plunger bore 111 is formed a pin hole 118 thatradially extends through, so that, with a retainer pin 119 inserted inthe pin hole 118 as shown in FIG. 1 to FIG. 3, the plunger 120 can befixed in its retracted position, to enable mounting of the tensionerincluding the plunger 120 assembled therein in the engine or any othersuch work.

The plunger 120 includes a plunger body 126, and a check valve 150 and areserve tube 130 provided inside the plunger body 126, as shown in FIG.4 and FIG. 5.

A connection/adjustment groove 122 is formed in the outer circumferenceof the plunger body 126, which forms a supply chamber 102 between itselfand the cylindrical surface 113 of the plunger bore 111 as shown in FIG.4, FIG. 5, and FIG. 8, and an outer leak groove 125 is provided in theouter circumference on the side of the oil pressure chamber 101 toextend from the oil pressure chamber 101 to the supply chamber 102.

Inside the plunger body 126 is arranged the reserve tube 130 having theoil reservoir chamber 123 on the side to which the plunger moves out,with the check valve 150 arranged on the oil pressure chamber 101 sideof the reserve tube 130.

The reserve tube 130 has a space inside that forms the oil reservoirchamber 123, and a small-diameter part 133 to form an internal supplycavity 127 between itself and the inner circumference of the plungerbody 126, with oil communication notches 135 formed at the distal end inthe outward direction of the plunger for supplying oil from the internalsupply cavity 127 to the oil reservoir chamber 123, as shown in FIG. 4,FIG. 5, and FIG. 9.

One end having an end face 131 on the check valve 150 side is formed asa large-diameter part 134 that snugly fits with the inner circumferenceof the plunger body 126. The oil reservoir chamber 123 communicates withthe check valve 150 through an oil hole 132 provided in the end face131.

The check valve 150 includes, as shown in FIG. 4 and FIG. 5, a ball seat151 seated on the end face 131 of the reserve tube 130, a check ball 152that can make sealing contact with the oil passage in the ball seat 151,and a retainer 153 that guides the check ball 152.

The urging unit accommodated inside the oil pressure chamber 101 such asto be able to expand and contract and to urge the plunger 120 outward isa coil spring 140, which is seated at one end on the bottom 112 of theplunger bore 111 and at the other end inside the plunger body 126 asshown in FIG. 4 to FIG. 7.

The other end of the coil spring 140 reaches the end face 131 of thereserve tube 130 via the outer circumference of the retainer 153 of thecheck valve 150 so as to efficiently use the depth of the inside of theplunger body 126 as the space for the coil spring 140 to expand andcontract.

The bottom 112 of the plunger bore 111 is formed as a circular flatsurface having the same diameter as that of the coil spring 140. Atapered surface 115 connects the bottom 112 with the cylindrical surface113 which makes sliding contact with the plunger 120.

One end of the coil spring 140 seated on the bottom 112 is restricted bythe tapered surface 115 from moving sideways to prevent looseness ordisplacement, so that the plunger 120 can reciprocate smoothly.

The tensioner body 110 is attached to a mounting wall portion (notshown) inside the engine that is present on the upper side in FIG. 2 oron the right side in FIG. 3, and the oil supply hole 114 is orientedtoward the mounting wall portion.

The connection/adjustment groove 122 of the plunger body 126 extends allaround the outer surface so that the supply chamber 102 formed betweenthe groove and the cylindrical surface 113 of the plunger bore 111 istubular.

The plunger hole 124 that communicates the internal supply cavity 127inside the plunger body 126 with the supply chamber 102 is oriented 180°opposite from the oil supply hole 114 in the cylindrical surface 113 ofthe plunger bore 111.

The oil communication notches 135 that communicate the oil reservoirchamber 123 with the internal supply cavity 127 are provided at thedistal end of the outward direction of the plunger.

The outer leak groove 125 in the outer circumference of the plunger body126 on the oil pressure chamber 101 side is located at the same phaseposition as that of the plunger hole 124 as shown in FIG. 5.

How the chain tensioner 100 according to the first embodiment of thepresent invention configured as described above operates will beexplained.

During normal operation, oil is constantly supplied from oil supplymeans provided in the mounting wall portion (not shown) through the oilsupply hole 114 so that the supply chamber 102 is always filled withoil.

The oil in the supply chamber 102 is fed into the oil reservoir chamber123 through the plunger hole 124, the internal supply cavity 127 and theoil communication notches 135 so that the oil reservoir chamber 123 isalso always filled with oil.

The check valve 150 allows the oil to flow in the direction from the oilreservoir chamber 123 into the oil pressure chamber 101. The oil in theoil reservoir chamber 123 is therefore supplied into the oil pressurechamber 101 through the check valve 150, so that the oil pressurechamber 101 is also always filled with oil.

Thus, the plunger 120 is urged outward also by the pressure of oil beingsupplied from the oil supply means provided in the mounting wall portion(not shown), in addition to the force from the coil spring 140.

When the plunger 120 is pushed inward, the check valve 150 closes, sothat oil flows from the oil pressure chamber 101 into the supply chamber102 through the gap between the plunger 120 and the cylindrical surface113 of the plunger bore 111. The flow resistance at this time provides adampening effect whereby the movement of the plunger 120 is dampened.

Next, how the tensioner operates immediately after the start-up afterbeing left a long time after the stop of oil supply (in the case with anengine, after the engine was stopped) will be described.

Since there is a time lag before oil is supplied immediately after thestart-up, no oil is supplied to the supply chamber 102 through the oilsupply hole 114 for a while, so that the tensioner has to operate onlywith the oil remaining in the oil pressure chamber 101 and the oilreservoir chamber 123.

When the plunger 120 is pushed inward, as compared to when there is noouter leak groove 125, oil can flow from the oil pressure chamber 101quickly into the supply chamber 102 through the gap between the plungerbody 126 and the cylindrical surface 113 of the plunger bore 111 becauseof the outer leak groove 125 where the flow resistance is somewhatlower.

On the other hand, in the gap between the plunger body 126 and thecylindrical surface 113 of the plunger bore 111 closer to the distal endthan the supply chamber 102, the flow resistance is much higher than inthe outer leak groove 125, so that most of the oil in the supply chamber102 does not leak out from the distal end but is recovered through theplunger hole 124, the internal supply cavity 127 and the oilcommunication notches 135 into the oil reservoir chamber 123.

The amount of oil leaking to the outside is thus reduced, so that theoil reservoir chamber 123 can have a smaller capacity to hold asufficient and necessary amount of oil during the time lag before oil issupplied at the restart.

Some of the oil leaking out from the oil pressure chamber 101 into thesupply chamber 102 flows out to the oil supply means through the oilsupply hole 114. However, since the oil supply means side of the oilsupply hole 114 is a sealed space, no large amount of oil flows outthere. Therefore, by restricting the amount of oil leaking out from thedistal end, a sufficient amount of oil can be recovered from the plungerhole 124 into the oil reservoir chamber 123.

In this embodiment, the plunger hole 124 and the outer leak groove 125are located at the same circumferential phase position, while the oilsupply hole 114 is located at a circumferentially different phaseposition from the plunger hole 124.

Therefore, more oil can be directed to the plunger hole 124 as it flowsinto the supply chamber 102 through the outer leak groove 125, and,since the oil path from the leak groove to the oil supply hole 114 islong, less oil flows out from the oil supply hole 114, so that more oilcan be recovered from the plunger hole 124 through the internal supplycavity 127 and the oil communication notches 135 into the oil reservoirchamber 123.

Since the plunger hole 124 is provided around the midpoint of theplunger body 126, and the oil communication notches 135 are located atthe distal end inside the plunger body 126, with the internal supplycavity 127 therebetween, oil leaks out less from the oil reservoirchamber 123 even after the supply of oil has stopped (in the case withan engine, after the engine was stopped), i.e., as more oil can beretained in the oil reservoir chamber 123, the tensioner can operatesmoothly even immediately after the start up after being left for a longtime.

<Embodiment 2>

The chain tensioner 200 according to a second embodiment of the presentinvention does not include an outer leak groove in the outercircumference of the plunger body 126 on the oil pressure chamber 101side, but instead includes inner leak grooves 136 in the large-diameterpart 134 of the reserve tube 130 as shown in FIG. 10 and FIG. 11, ascompared to the chain tensioner 100 according to the previouslydescribed first embodiment (reference numerals in the drawings are thesame as those of the first embodiment).

In this embodiment, the reserve tube 130 is formed with inner leakgrooves 136 at four positions of the large-diameter part 134 as shown inFIG. 11, so that oil can flow from the oil pressure chamber 101 throughthe inner leak grooves 136 into the internal supply cavity 127.

No leak grooves are formed in the outer circumference on the oilpressure chamber 101 side of the plunger body 126.

The chain tensioner is configured the same in other respects as thechain tensioner 100 according to the previously described firstembodiment.

The chain tensioner 200 according to the second embodiment of thepresent invention configured as described above works in normaloperation similarly to the chain tensioner 100 according to thepreviously described first embodiment.

One difference from the chain tensioner 100 of the first embodiment ishow the oil flows immediately after the start-up after being left for along time after the stop of the oil supply (in the case with an engine,after the engine was stopped).

Since the flow resistance of oil leaking through the inner leak grooves136 into the internal supply cavity 127 is smaller than the flowresistance of oil flowing from the oil pressure chamber 101 through thegap between the plunger body 126 and the cylindrical surface 113 of theplunger bore 111 into the supply chamber 102, when the plunger 120 ispushed inwards, most oil flows through the inner leak grooves 136 intothe internal supply cavity 127, and is recovered into the oil reservoirchamber 123 through the oil communication notches 135.

The amount of oil leaking to the outside is thus reduced, so that theoil reservoir chamber 123 can have a smaller capacity to hold asufficient and necessary amount of oil during the time lag before oil issupplied at the restart.

While the inner leak grooves 136 are provided at four positions in thelarge-diameter part 134 in the embodiment above, the grooves may beprovided at three or less positions, or five or more positions.

<Embodiment 3>

The chain tensioner 300 according to a third embodiment of the presentinvention does not include an outer leak groove in the outercircumference of the plunger body 126 on the oil pressure chamber 101side, but instead includes end face leak grooves 137 and seat leakgrooves 154 in the end face 131 of the reserve tube 130 and in thesurface on the reserve tube 130 side of the ball seat 151, respectively,as shown in FIG. 12, FIG. 13A, and FIG. 13B, as compared to the chaintensioner 200 according to the previously described second embodiment(reference numerals in the drawings are the same as those of the firstembodiment).

In this embodiment, the reserve tube 130 is formed with end face leakgrooves 137 at three radial positions in the end face 131, which extendfrom the outer circumference to the oil hole 132, as shown in FIG. 13A,and with seat leak grooves 154 at three radial positions similarly inthe surface on the reserve tube 130 side of the ball seat 151, as shownin FIG. 13B.

The end face leak grooves 137 and the seat leak grooves 154 arepositioned opposite each other as shown in FIG. 12 so that oil can flowfrom the oil pressure chamber 101 through the end face leak grooves 137and the seat leak grooves 154 into the internal supply cavity 127.

No leak grooves are formed in the outer circumference on the oilpressure chamber 101 side of the plunger body 126.

The chain tensioner is configured the same in other respects as thechain tensioner 100 according to the previously described firstembodiment.

The chain tensioner 300 according to the third embodiment of the presentinvention configured as described above works in normal operationsimilarly to the chain tensioner 100 according to the previouslydescribed first embodiment.

The oil flow immediately after the start-up after being left for a longtime after the stop of the oil supply (in the case with an engine, afterthe engine was stopped) is different from that in the chain tensioner100 of the first embodiment, and the same as that in the chain tensioner200 of the second embodiment.

Since the flow resistance of oil leaking through the end face leakgrooves 137 and the seat leak grooves 154 into the internal supplycavity 127 is smaller than the flow resistance of oil flowing from theoil pressure chamber 101 through the gap between the plunger body 126and the cylindrical surface 113 of the plunger bore 111 into the supplychamber 102, when the plunger 120 is pushed inwards, most oil flowsthrough the end face leak grooves 137 and the seat leak grooves 154 intothe internal supply cavity 127, and is recovered into the oil reservoirchamber 123 through the oil communication notches 135.

The amount of oil leaking to the outside is thus reduced, so that theoil reservoir chamber 123 can have a smaller capacity to hold asufficient and necessary amount of oil during the time lag before oil issupplied at the restart.

While the end face leak grooves 137 and seat leak grooves 154 are bothprovided at three locations in the embodiment above, the grooves may beprovided at two or less positions, or four or more positions.

While the end face leak grooves 137 and seat leak grooves 154 arepositioned opposite each other, they need not necessarily face eachother, and may be provided in different numbers if they are not oppositeeach other, or one of the end face leak grooves 137 and seat leakgrooves 154 may be omitted.

<Embodiment 4>

The chain tensioner 400 according to a fourth embodiment of the presentinvention does not have a ball seat 151 as compared to the chaintensioner 200 according to the previously described second embodiment,as shown in FIG. 14 (reference numerals in the drawing are the same asthose of the second embodiment).

In this embodiment, the check ball 152 directly contacts the oil hole132 in the end face 131 of the reserve tube 130, so that the end facefunctions as the ball seat.

With this embodiment, the number of components can be reduced to achievea reduction in size and weight, and also, more oil can be retained byefficient use of space, as the oil reservoir chamber 123 is made largerby the thickness of the ball seat.

<Embodiment 5>

The chain tensioner 450 according to a fifth embodiment of the presentinvention has the connection/adjustment groove that forms the supplychamber 102 of oil in the inner circumference of the plunger bore asshown in FIG. 15, as compared to the chain tensioner 200 according tothe previously described second embodiment (same elements and componentsare given the same reference numerals as those of the second embodiment.The inner leak grooves are not shown).

In this embodiment, a body-side connection/adjustment groove 103 isformed in the inner circumference of the plunger bore 111 of thetensioner body 110 to form the supply chamber 102 between the boresurface and the outer circumference of the plunger body 126.

With this embodiment, the plunger body 126 can have a smaller thicknessto reduce its weight, as it has a cylindrical shape with flat surfacesboth inside and outside without any protrusions or recesses as shown inFIG. 15, and as the plunger body 126 does not require much processing,it can be readily produced without a complex process, such as pressingor the like.

End face leak grooves 137 and seat leak grooves 154 similarly to thethird embodiment may be provided instead of the inner leak grooves (notshown).

While specific examples of the chain tensioner according to the presentinvention have been described in the embodiments above, the chaintensioner according to the present invention is not limited to theseexamples, and the shapes, positions, sizes, and positional relationshipswith each other of various constituent parts may be changed in variousmanners.

For example, while the connection/adjustment groove 122 or the body-sideconnection/adjustment groove 103 extends all around in the embodimentsdescribed above so that the supply chamber 102 is tubular, theconnection/adjustment groove 122 or the body-side connection/adjustmentgroove 103 may be formed only in part (in such a shape as, for example,the connection/adjustment groove 123 of Japanese Patent Publication No.4376278 mentioned above), so that the supply chamber 102 does not extendall around, as long as oil can be supplied during normal operation andrecovered into the oil reservoir chamber 123 at start-up.

The outer leak groove 125, inner leak grooves 136, end face leak grooves137, and seat leak grooves 154 in various embodiments may have anycross-sectional shape, depth, circumferential width, and the like, whichmay be selected suitably in accordance with the environment of itsapplication, as long as it serves the purpose of the present inventionand works as described above.

Other components commonly included in a chain tensioner, such as aratchet mechanism, may of course be added to the configurations of theembodiments described above.

The chain tensioner of the present invention may not necessarily beapplied to a chain guide mechanism that uses a guide shoe for slidablyguiding a transmission chain such as an endless roller chain passingover respective sprockets of a crankshaft and a cam shaft in an engineroom, but may also be adopted in applications where the chain isslidably guided by the distal end of the plunger.

The chain tensioner may not necessarily be applied to a chaintransmission mechanism but also used for similar transmission mechanismsthat use belts, ropes and the like. The chain tensioner of the presentinvention, including a tensioner body having a cylindrical plunger borewith an open end, a cylindrical plunger slidable within the plungerbore, and an urging unit accommodated inside an oil pressure chamberformed between the plunger bore and a rear end of the plunger such as tobe able to expand and contract and to urge the plunger outward, isapplicable for use in various industrial fields where sufficient oilneeds to be supplied at restart after a long time after the stop of oilsupply.

What is claimed is:
 1. A chain tensioner comprising: a tensioner bodyhaving a cylindrical plunger bore with an open end; a cylindricalplunger slidable within the plunger bore; and an urging unitaccommodated inside an oil pressure chamber formed between the plungerbore and a rear end of the plunger such as to be able to expand andcontract and to urge the plunger outward, the plunger including aplunger body, and a check valve and a reserve tube provided inside theplunger body, and the reserve tube having an oil hole provided on oneside closer to the check valve and an oil reservoir chambercommunicating with the oil pressure chamber through the oil hole, and aconnection/adjustment groove formed at least in one of an outercircumferential surface of the plunger body and an inner circumferentialsurface of the plunger bore to form an oil supply chamber; an oil supplyhole formed in the tensioner body, for supplying oil to the supplychamber; an internal supply cavity formed between an outercircumferential surface of a small-diameter part of the reserve tube andan inner circumferential surface of the plunger body; a plunger holeformed in the plunger body, for supplying oil from the supply chamber tothe internal supply cavity; and an oil communication notch formed at adistal end in an outward direction of the plunger of the reserve tube,for supplying oil from the internal supply cavity to the oil reservoirchamber.
 2. The chain tensioner according to claim 1, further comprisingan outer leak groove formed in the outer circumferential surface of theplunger body on one side closer to the oil pressure chamber such as toextend from the oil pressure chamber to the supply chamber.
 3. The chaintensioner according to claim 2, wherein the outer leak groove is locatedat a circumferentially same phase position as the plunger hole.
 4. Thechain tensioner according to claim 1, further comprising an inner leakgroove formed in the outer circumferential surface of the reserve tubeon one side closer to the check valve such as to extend from the oilpressure chamber to the internal supply cavity.
 5. The chain tensioneraccording to claim 1, further comprising a contact surface leak grooveformed in at least one of opposite surfaces of the reserve tube and thecheck valve such as to extend from the oil pressure chamber to the oilreservoir chamber.
 6. The chain tensioner according to claim 1, whereinthe urging unit includes a coil spring having one end seated on a bottomof the plunger bore and the other end seated in the plunger body.
 7. Thechain tensioner according to claim 6, wherein the check valve includes aball seat, a check ball capable of making sealing contact with an oilpassage in the ball seat, and a retainer that guides the check ball, theother end of the coil spring being seated on an outer flange of theretainer in the plunger body.
 8. The chain tensioner according to claim7, wherein the surface of the reserve tube on one side closer to thecheck valve functions as the ball seat of the check valve.
 9. The chaintensioner according to claim 6, wherein the bottom of the plunger boreis formed as a circular flat surface with a same diameter as the coilspring, and has a tapered surface that connects the bottom with thecylindrical surface sliding with the plunger.